The heavens above: a popular handbook of astronomy (1882)
Gillet, J. A. (Joseph Anthony), 1837-1908 · New York, Chicago, Potter, Ainsworth, & Co. · leaf 202
umbral filaments are curved spirally, indicating a cyclonicaction, as shown in Fig. 195. In such cases the whole spotusually turns slowly around, sometimes completing an entirerevolution in a few days. More frequently, however, thespiral motion lasts but a short time ; and occasionally,… … Fig- 195- Neighboring spots show no tendency to rotate in the
Astronomy
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